Preparation method of a composite antioxidant and application thereof

Abstract

The application discloses a preparation method of a composite antioxidant and application thereof, and belongs to the field of high polymer materials. In the application, a ring octene and a silicon-containing cyclic olefin monomer are subjected to metathesis copolymerization under the action of a metathesis catalyst, a silicon-containing polymer is obtained after chemical hydrogenation, and then the composite antioxidant is obtained after hydrolysis and mixing with lignin. The main chain of the composite antioxidant is a saturated hydrocarbon chain, the compatibility with polyethylene is high, the silicon-containing polymer is hydrolyzed to generate active silanol, the active silanol is efficiently bonded with lignin, and the lignin provides natural polyphenol antioxidant function. The application realizes efficient antioxidant of the composite material, high compatibility and long-term durability, and provides a new idea for high-performance environment-friendly high polymer composite materials.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials, specifically relating to a method for preparing a composite antioxidant and its application. Background Technology

[0002] Polyethylene (PE) is the simplest and most widely used general-purpose thermoplastic, possessing advantages such as readily available raw materials, low density, good mechanical properties, chemical resistance, and ease of processing and molding. It occupies an important position in packaging, pipes, films, and structural materials. However, due to its relatively low melting temperature and the presence of easily oxidized sites such as tertiary carbons in its molecular chains, PE is highly susceptible to thermo-oxidative free radical chain degradation during high-temperature processing and use. This leads to molecular chain breakage, structural damage, and performance deterioration. To prevent oxidative degradation of the polymer, antioxidants are typically added during its synthesis or processing.

[0003] In polyolefin processes, it is common practice to add antioxidants to the polyolefin product immediately after polymerization. Lignin is a natural, renewable, and non-toxic polyphenolic free radical scavenging antioxidant. However, due to its strong polarity, poor dispersibility, and poor thermal stability, direct addition of lignin to polyethylene can lead to poor interfacial compatibility, poor dispersibility, and easy migration. Composite antioxidants, on the other hand, not only achieve good interfacial bonding with the polyethylene matrix but also endow polyolefin materials with excellent thermo-oxidative stability and long-term anti-aging properties. Summary of the Invention

[0004] This invention addresses the problems existing in the prior art by providing a method for preparing a composite antioxidant and its application. The composite antioxidant of this invention exhibits excellent thermal oxidation stability, high compatibility, and long-term durability.

[0005] The preparation method of the composite antioxidant of the present invention includes the following steps:

[0006] Step 1: Cyclooctene and silicon-containing cyclic olefin monomers undergo metathesis copolymerization under the action of a metathesis catalyst, and then obtain a silicon-containing polymer after chemical hydrogenation reaction;

[0007] Step 2: The silicon-containing polymer is hydrolyzed and mixed with lignin to undergo a condensation reaction, thereby obtaining a composite antioxidant.

[0008] In step 1, the silicon-containing cyclic olefin monomer is selected from one or more compounds with the following structures:

[0009] .

[0010] The silicon-containing polymer is selected from one or more compounds with the following structures:

[0011] ,

[0012] ,

[0013] .

[0014] Furthermore, the molar ratio of the cyclooctene monomer to the silicon-containing cyclic olefin monomer is 100:1-10, preferably 100:10.

[0015] In step 1, the metathesis catalyst is a second-generation Grubbs catalyst (GⅡ).

[0016] Furthermore, the molar amount of the metathesis catalyst is 0.01-0.1% of the molar amount of the cyclooctene monomer, preferably 0.05%.

[0017] In step 1, the reaction temperature of the metathesis copolymerization reaction is 20-40℃, and the reaction time is 4-12h. Preferably, the reaction temperature is 40℃ and the reaction time is 6h.

[0018] In step 1, p-toluenesulfonyl hydrazine and tri-n-propylamine are added to the system for a chemical hydrogenation reaction. The mass ratio of the metathesis polymer obtained after the metathesis copolymerization reaction to p-toluenesulfonyl hydrazine and tri-n-propylamine is 1:3:3.

[0019] Furthermore, the chemical hydrogenation reaction is carried out at a temperature of 140°C for a time of 12-24 hours.

[0020] In step 2, the condensation reaction is carried out at a temperature of 85-90℃ for 12-24 hours, and the pH of the system is 4.5-5.5.

[0021] Furthermore, the mass ratio of the hydrogenated polymer obtained after hydrolysis to lignin is 1:1-5.

[0022] The preparation method of the composite antioxidant of the present invention is illustrated with specific steps as follows:

[0023] (1) Under a nitrogen atmosphere, silicon-containing cyclic olefin monomers and cyclooctene are dissolved in dichloromethane, and then a metathesis catalyst is added to carry out a metathesis copolymerization reaction. After the reaction is completed, the solvent is concentrated, methanol is added to precipitate the polymer, and the polymer is filtered, washed, and dried to obtain the metathesis polymer.

[0024] (2) Under a nitrogen atmosphere, p-toluenesulfonyl hydrazine and tri-n-propylamine, as well as xylene solvent, were added to the obtained metathesis polymer. The mixture was refluxed at 140°C for 12-24 h. After the hydrogenation reaction was completed, methanol was added to precipitate the polymer. The polymer was then filtered and dried to obtain a silicon-containing polymer.

[0025] (3) Disperse lignin evenly in ethanol and aqueous solution (V EtOH :VH2O =1:4), adjust the pH of the system to 5.0 with glacial acetic acid, add the silicon-containing polymer to the reaction apparatus, reflux at 85-90℃ for 12-24 h, filter, wash, and dry to obtain the composite antioxidant.

[0026] The composite antioxidant prepared by this invention has the following structure, depending on the selected monomer:

[0027]

[0028]

[0029]

[0030] Where m and n are the number of polyolefin segments, and both m and n are positive numbers.

[0031] Preferably, the m:n ranges from 1 to 10:100.

[0032] The application of the composite antioxidant of this invention in the preparation of polyethylene.

[0033] Specifically, the composite antioxidant is added during the preparation of polyethylene materials to improve the thermal oxidation stability and long-term durability of the materials.

[0034] Furthermore, the mass ratio of the composite antioxidant to polyethylene is 0.4:9.6.

[0035] The silicon-containing cyclic olefin monomers used in this invention are selected from one or more of M1, M2, and M3. These monomers are prepared by the following method:

[0036] Silicon-containing cyclic olefin monomer M1: obtained by amidation reaction of 5-norbornene-2-carboxylic acid (compound I) and (3-aminopropyl)triethoxysilane (compound IV).

[0037] Silicon-containing cyclic olefin monomer M2: obtained by substitution reaction of 5-norbornene-2-methanol (compound II) and triethoxysilane chloride (compound V).

[0038] Silicon-containing cyclic olefin monomer M3: obtained by substitution reaction of 4-hydroxycyclooctene (compound III) and triethoxysilane chloride (compound V).

[0039]

[0040] Furthermore, the method for preparing the silicon-containing cyclic olefin monomer M1 includes the following steps:

[0041] Under a nitrogen atmosphere at 0 °C, 5-norbornene-2-carboxylic acid, (3-aminopropyl)triethoxysilane, and 4-dimethylaminopyridine (DMAP) were dissolved in tetrahydrofuran solvent. Then, a dichloromethane solution of 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC·HCl) was added, and the reaction was carried out at room temperature. The mixture was concentrated and purified by column chromatography to obtain the target monomer product M1.

[0042] The preferred molar ratio of 5-norbornene-2-carboxylic acid to (3-aminopropyl)triethoxysilane is 1:1-1.2, and the reaction time is 12-24 h.

[0043] Furthermore, the method for preparing the silicon-containing cyclic olefin monomer M2 includes the following steps:

[0044] 5-norbornene-2-methanol and triethoxysilane chloride were dissolved together in dichloromethane solvent at 0 °C under a nitrogen atmosphere. Triethylamine was then added, and the mixture was reacted at room temperature. The reaction was then filtered, concentrated, and purified by column chromatography to obtain the target monomer product M2.

[0045] The preferred molar ratio of 5-norbornene-2-methanol to triethoxysilane chloride is 1:1-1.2, and the reaction time is 12-24 h.

[0046] Furthermore, the method for preparing the silicon-containing cyclic olefin monomer M3 includes the following steps:

[0047] 4-hydroxycyclooctene and triethoxysilane chloride were dissolved together in dichloromethane solvent at 0 °C under a nitrogen atmosphere. Triethylamine was then added, and the mixture was reacted at room temperature. The reaction was then filtered, concentrated, and purified by column chromatography to obtain the target monomer product M3.

[0048] The preferred molar ratio of 4-hydroxycyclooctene to triethoxysilane chloride is 1:1-1.2, and the reaction time is 12-24 h.

[0049] The present invention does not limit the source of the above-mentioned compounds.

[0050] Based on the above technical solution, the beneficial effects of the present invention are as follows:

[0051] The preparation method of this invention is simple and convenient, with high metathesis reaction efficiency. The main chain is a saturated hydrocarbon chain, providing good compatibility with polyethylene. The silicon-containing polymer hydrolyzes to generate active silanol, which bonds efficiently with lignin. At the same time, lignin provides natural polyphenol antioxidant functions. This achieves high-efficiency antioxidant properties, high compatibility, and long-term durability in the composite material, providing a new approach for high-performance environmentally friendly polymer composite materials. Attached Figure Description

[0052] Figure 1 The 1H NMR spectrum of M1 prepared in Example 1 (1 (H NMR) image.

[0053] Figure 2 The carbon NMR spectrum of M1 prepared in Example 1 ( 13 (C NMR) diagram.

[0054] Figure 3 M2 prepared in Example 1 1 H NMR spectrum.

[0055] Figure 4 M2 prepared in Example 1 13 C NMR spectrum.

[0056] Figure 5 The 1H NMR spectrum of M3 prepared in Example 1 ( 1 (H NMR) image.

[0057] Figure 6 The carbon NMR spectrum of M3 prepared in Example 1 ( 13 (C NMR) diagram.

[0058] Figure 7 The metathesis polymer u-P1 prepared in Example 2 1 H NMR spectrum.

[0059] Figure 8 The metathesis polymer u-P2 prepared in Example 2 1 H NMR spectrum.

[0060] Figure 9 The metathesis polymer u-P3 prepared in Example 2 1 H NMR spectrum.

[0061] Figure 10 The infrared spectrum of the composite antioxidant prepared in Example 3.

[0062] Figure 11 The diagram shows the dynamic mechanical analysis of the composite antioxidant / HDPE composite material prepared in Example 4.

[0063] Figure 12 Thermodynamic analysis diagram of the composite antioxidant / HDPE composite material prepared in Example 4.

[0064] Figure 13 The diagram shows the oxidation-induced temperature of the composite antioxidant / HDPE composite material prepared in Example 4.

[0065] Figure 14 Thermodynamic analysis diagram of the simple mixed HDPE of silicon-containing polymer and lignin prepared in Example 5.

[0066] Figure 15 The oxidative induction temperature analysis diagram is shown for the simple mixed HDPE of silicon-containing polymer and lignin prepared in Example 5. Detailed Implementation

[0067] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of the invention. In the following detailed description, numerous specific details are set forth to provide a thorough understanding of the embodiments of the invention for ease of explanation. However, it will be apparent that one or more embodiments may be practiced without these specific details. Furthermore, descriptions of well-known structures and techniques are omitted in the following description to avoid unnecessarily obscuring the concept of the invention.

[0068] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention. The term "comprising" as used herein indicates the presence of features, steps, or operations, but does not exclude the presence or addition of one or more other features.

[0069] In this invention, "independently" means that when there are multiple subjects, they can be the same or different from each other.

[0070] In realizing the concept of this invention, it was discovered that although phenolic antioxidants such as lignin can alleviate the degradation of polyethylene by capturing free radicals, these additives are incompatible with the polymer matrix, causing them to migrate out of the polymer matrix. This defect not only reduces their protective efficacy but may also cause potential environmental problems.

[0071] Lignin can be efficiently bonded to the polymer chain via chemical methods, thereby significantly improving the thermo-oxidative stability of polyolefins. The preparation method of this composite antioxidant includes: a metathesis copolymerization reaction of cyclooctene and a silicon-containing cyclic olefin monomer under the action of a metathesis catalyst; chemical hydrogenation to obtain a silicon-containing polymer; and then hydrolysis followed by mixing with lignin to obtain the composite antioxidant. The composite antioxidant prepared by this invention exhibits excellent thermo-oxidative stability, high compatibility, and long-term durability.

[0072] Specifically, according to one aspect of the present invention, a method for preparing a composite antioxidant is provided, comprising: cyclooctene and a silicon-containing cyclic olefin monomer undergoing a metathesis copolymerization reaction under the action of a metathesis catalyst, obtaining a silicon-containing polymer after chemical hydrogenation, and then mixing it with lignin after hydrolysis to obtain a composite antioxidant.

[0073] The preparation method of this invention is simple and convenient, employing a metathesis reaction for copolymerization, which is simple, convenient, and highly efficient. The saturated hydrocarbon main chain provides good compatibility with polyethylene. The silicon-containing polymer hydrolyzes to generate active silanols, which efficiently bond with lignin. Compared to directly adding lignin, the method of this invention has higher grafting dispersion and compatibility, resulting in better product performance. Simultaneously, lignin provides natural polyphenol antioxidant functions; the phenolic hydroxyl groups in the phenolic group are highly efficient free radical scavengers, inhibiting thermo-oxidative aging and degradation of polyethylene during high-temperature processing and use, thus extending the material's service life. Furthermore, lignin is a naturally occurring polymer material, meeting the requirements of green chemistry and providing a new approach for high-performance, environmentally friendly polymer composite materials.

[0074] The present invention will now be described in further detail with reference to specific embodiments. The given embodiments are merely illustrative of the invention and not intended to limit its scope. The embodiments provided below can serve as a guide for further improvements by those skilled in the art and do not constitute a limitation on the invention in any way.

[0075] Unless otherwise specified, the experimental methods used in the following examples are conventional methods, performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Unless otherwise specified, the materials and reagents used in the following examples are commercially available.

[0076] Example 1: Preparation of silicon-containing cyclic olefin monomers M1, M2, and M3

[0077] 1. The preparation method of M1 includes the following steps:

[0078] Under a nitrogen atmosphere, 5-norbornene-2-carboxylic acid (20.0 mmol), (3-aminopropyl)triethoxysilane (22.0 mmol), and DMAP (4 mmol) were dissolved in 100 mL of dichloromethane. The temperature was lowered to 0 °C, and then 10 mL of LEDC·HCl (30.0 mmol) dichloromethane solution was added. After the reaction was restored to room temperature, it was continued for 12 h. The product was concentrated and purified by column chromatography to obtain the target product M1 in 62% yield. M1... 1 H NMR (CDCl3) plot, 13 The C NMR (CDCl3) spectra are as follows: Figure 1 and Figure 2 As shown.

[0079] The reaction route is shown below:

[0080] .

[0081] 2. The preparation method of M2 includes the following steps:

[0082] Under a nitrogen atmosphere, 5-norbornene-2-methanol (20.0 mmol) and triethoxysilane chloride (22.0 mmol) were dissolved in 100 mL of dichloromethane. The temperature was lowered to 0 °C, and then a dichloromethane solution of triethylamine (30.0 mmol) was added. The reaction was allowed to return to room temperature and continued for 12 h. After the reaction was complete, the filtrate was filtered. The concentrate was then purified by column chromatography to obtain the target product M2 in 76% yield. M2... 1 H NMR (CDCl3) plot and 13 The C NMR (CDCl3) spectra are as follows: Figure 3 and Figure 4 As shown.

[0083] The reaction route is shown below:

[0084] .

[0085] 3. The preparation method of M3 includes the following steps:

[0086] Under a nitrogen atmosphere, 20.0 mmol of 4-hydroxycyclooctene and 22.0 mmol of triethoxysilane chloride were dissolved in 100 mL of dichloromethane. The temperature was lowered to 0 °C, and then a dichloromethane solution of 30.0 mmol of triethylamine was added. The reaction was allowed to return to room temperature and continued for 12 h. After the reaction was complete, the filtrate was filtered. The filtrate was concentrated and purified by column chromatography to obtain the target product M3 in 70% yield. M3 contained... 1 H NMR (CDCl3) plot and 13 The C NMR (CDCl3) spectra are as follows: Figure 5 and Figure 6 As shown.

[0087] The reaction route is shown below:

[0088] .

[0089] Example 2: Preparation of Silicon-Containing Polymers

[0090] Under a nitrogen atmosphere, 20 mmol of cyclooctene monomer, 2 mmol of the silane-containing olefin monomer M1 prepared in Example 2, and 100 mL of anhydrous dichloromethane were added to a 200 mL Schlenk reaction flask. The reaction flask was placed in a 40 °C oil bath. Then, 10 μmol of Grubbs second-generation catalyst was dissolved in 1 mL of dichloromethane and injected into the reaction flask. The reaction was continued for 6 h. After the reaction was completed, the solvent was concentrated, 200 mL of methanol was added to precipitate the polymer, and the polymer was obtained by filtration, washing, and drying to obtain the metathesis polymer u-P1.

[0091] By replacing M1 with a silicon-containing olefin monomer M2 and using the same method described above, metathesis polymer u-P2 was prepared.

[0092] By replacing M1 with a silicon-containing olefin monomer M3 and using the same method described above, metathesis polymer u-P3 was prepared.

[0093] The metathesis polymer u-P1 was added to a 200 mL reaction flask, along with 6.0 g of p-toluenesulfonyl hydrazine, 6.0 g of tri-n-propylamine, and 10 mL of xylene solvent. After reacting for 12 h under a nitrogen atmosphere, 300 mL of methanol was added to the reaction flask to precipitate the polymer. The polymer was then filtered and dried to obtain approximately 2.0 g of silicon-containing polymer P1.

[0094] By replacing u-P1 with metathesis polymer u-P2 and using the same method described above, silicon-containing polymer P2 was prepared.

[0095] By replacing u-P1 with metathesis polymer u-P3 and using the same method described above, silicon-containing polymer P3 was prepared.

[0096] 1H NMR spectrum 1 H NMR (CDCl3) such as Figure 7 , 8 As shown in Figures 9 and 9.

[0097] Example 3: Preparation of a composite antioxidant

[0098] 5g of lignin was dispersed in an ethanol / water mixture (volume ratio 1:4) and ultrasonically dispersed for 10 min. The pH of the system was adjusted to 4.5-5.5 with glacial acetic acid. 1g of a silicon-containing polymer was added, and the mixture was refluxed and stirred at 85-90℃ for 12 h. The reaction product was filtered, washed with water, and dried at 60℃ to obtain the composite antioxidants (A1, A2, A3). Their infrared spectra are shown below. Figure 10 As shown. By Figure 10 It is known that the antioxidant in the composite material contains hydroxyphenyl, eugenyl, and Si-OC, indicating that lignin successfully reacted with the silicon-containing polymer.

[0099] Example 4:

[0100] 0.4 g of the composite antioxidants (A1, A2, A3) and 10.0 g of HDPE were weighed and mixed using a twin-screw extruder to obtain dumbbell-shaped specimens with a length of 5.0 cm, a width of 4.0 mm (at its narrowest point), and a thickness of 1.0 mm, respectively labeled HDPE / A1, HDPE / A2, and HDPE / A3. HDPE served as the control group. Stress / strain tests were conducted at room temperature at a speed of 50 mm / min according to the standard test method ASTM D638. At least three specimens were tested for each sample.

[0101] Example 5:

[0102] 0.2 g of silicon-containing polymers (P1, P2, P3) and 0.2 g of lignin were weighed and mixed with 10.0 g of HDPE through a twin-screw extruder to obtain dumbbell-shaped specimens with a length of 5.0 cm, a width of 4.0 mm (narrowest point), and a thickness of 1.0 mm. These specimens were denoted as HDPE / P1 / lignin, HDPE / P2 / lignin, and HDPE / P3 / lignin, respectively.

[0103] The dynamic mechanical properties of the material sample obtained in Example 4 are as follows: Figure 11 As shown, the thermodynamic properties are as follows Figure 12 As shown, the DSC spectrum is as follows Figure 13 As shown. The thermodynamic properties of the material sample obtained in Example 5 are as follows. Figure 14 As shown, the DSC spectrum is as follows Figure 15 As shown.

[0104] Depend on Figure 11 It can be seen that the addition of antioxidants to composite materials does not affect the mechanical properties of HDPE itself.

[0105] Depend on Figure 12 It can be seen that the degradation temperature of HDPE / A1 to 95% is 368.6℃; the degradation temperature of HDPE / A2 to 95% is 351.8℃; and the degradation temperature of HDPE / A3 to 95% is 353.5℃. Compared with the degradation temperature of HDPE itself (338.3℃), this is 10-30℃ higher, indicating that the antioxidant in the composite material has excellent thermo-oxidative stability.

[0106] Depend on Figure 13 It can be seen that the oxidation induction temperature of HDPE / A1 is 215.2℃; the oxidation induction temperature of HDPE / A2 is 203.3℃; and the oxidation induction temperature of HDPE / A3 is 216.8℃, which is better than that of HDPE (190.2℃), indicating that the antioxidant of the composite material has excellent antioxidant properties.

[0107] Depend on Figure 14 It can be seen that the degradation temperature of HDPE / P1 / lignin to 95% is 351.5℃; the degradation temperature of HDPE / P2 / lignin to 95% is 351.8℃; and the degradation temperature of HDPE / P3 / lignin to 95% is 348.9℃. Compared with antioxidants in composite materials (351.8-368.6℃), this strategy is superior to simple mixing and addition.

[0108] Depend on Figure 15It can be seen that the oxidation induction temperature of HDPE / P1 / lignin is 194.8℃; the oxidation induction temperature of HDPE / P2 / lignin is 194.2℃; and the oxidation induction temperature of HDPE / P3 / lignin is 192.3℃. Compared with antioxidants in composite materials (203.3-216.8℃), this strategy is superior to simple mixing and addition.

[0109] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a composite antioxidant, characterized in that... Includes the following steps: Step 1: Cyclooctene and silicon-containing cyclic olefin monomers undergo metathesis copolymerization under the action of a metathesis catalyst, and then obtain a silicon-containing polymer after chemical hydrogenation reaction; Step 2: The silicon-containing polymer is hydrolyzed and mixed with lignin to undergo a condensation reaction, thereby obtaining a composite antioxidant; In step 1, the silicon-containing cyclic olefin monomer is selected from one or more compounds with the following structures: 。 2. The preparation method according to claim 1, characterized in that: In step 1, the molar ratio of the cyclooctene monomer to the silicon-containing cyclic olefin monomer is 100:1-10.

3. The preparation method according to claim 1, characterized in that: In step 1, the metathesis catalyst is a second-generation Grubbs catalyst.

4. The preparation method according to claim 1, characterized in that: In step 1, the reaction temperature of the metathesis copolymerization reaction is 20-40℃, and the time is 4-12h.

5. The preparation method according to claim 1, characterized in that: In step 1, p-toluenesulfonyl hydrazine and tri-n-propylamine are added to the system to carry out a chemical hydrogenation reaction.

6. The preparation method according to claim 5, characterized in that: The chemical hydrogenation reaction is carried out at a temperature of 140°C for 12-24 hours.

7. The preparation method according to claim 1, characterized in that: In step 2, the condensation reaction is carried out at a temperature of 85-90℃ for 12-24 hours, and the pH of the system is 4.5-5.

5.

8. A composite antioxidant, prepared according to any one of claims 1-7, characterized in that... The structure of the composite antioxidant is selected from one or more of the following general formulas: 、 、 ； Where m and n are both positive numbers, and the ratio of m to n is between 1 and 10:

100.

9. The application of the composite antioxidant of claim 8 in the preparation of polyethylene.

10. The application according to claim 9, characterized in that: During the preparation of polyethylene material, the composite antioxidant is added to improve the thermal oxidation stability and long-term durability of the material; the mass ratio of the composite antioxidant to polyethylene is 0.4:9.6.

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